For photoconductive materials to constitute a light receiving layer of a light receiving member for use in an image-forming field, it is required that they have high sensitivity, high S/N ratio (photocurrent (IP)/dark current (ID)), absorption spectrum characteristics suited to electromagnetic waves to be irradiated, rapid responsivity to light and desired dark resistance, as well as they are not harmful to human bodies. In particular, for light receiving members to be employed in electrophotographic apparatus which are used as business machines at the office, it is important that they cause no public pollution during use.
From these stand points, public attention has been focused recently on photoconductive materials comprising amorphous silicon (hereinafter referred to "a-Si"), for example, as described in Offenlegungsschrifts No. 2746967 and 2855718, which disclose the use of them in electrophotographic light receiving members.
FIG. 2 is a cross sectional view schematically illustrating the layer constitution of a known electrophotographic light receiving member 200, in which are shown a conductive substrate 201 and a light receiving layer 202 comprising a-Si. The electrophotographic light receiving member is generally prepared by forming a photosensitive layer 202 comprising a-Si on a conductive substrate 201 by means of a film-forming method such as vapor deposition, sputtering, ion plating, terminal CVD, optical CVD or plasma CVD process while maintaining the conductive substrate at a temperature of 50.degree. C. to 400.degree. C. Among these film-forming methods for the formation of the photoconductive layer, the plasma CVD process, that is, a method of decomposing a raw material gas in glow discharge by direct current, radio frequency or microwave energy and forming an a-Si deposited layer on the conductive substrate has been put to practical use as a preferred method.
In Offenlegungsschrift No. 3046509, an electrophotographic light receiving member comprising a conductive substrate and a photoconductive layer comprising a-Si containing halogen atoms as a constituent element (hereinafter referred to as "a-Si:X") being disposed on said conductive substrate has been proposed. In this publication, it is stated that dangling bonds are compensated by incorporating 1 to 40 atomic % of halogen atoms into a-Si, to reduce the localized level density in the energy gap and obtain electrical and optical characteristics suitable as the photoconductive layer for the electrophotographic light receiving layer.
On the other hand, it has been known for amorphous silicon carbides (hereinafter referred to as "a-SiC") that they have higher heat resistance and surface hardness, and higher dark resistivity as compared with a-Si, and the optical band gap of them can be varied within a range from 0.6 to 0.8 depending on the carbon content. An electrophotographic light receiving member in which the photoconductive layer is constituted with such a-SiC is proposed in U.S. Pat. No. 4,471,042. This patent literature discloses that electrophotographic characteristics including high dark resistance and satisfactory light sensitivity are provided when the photoconductive layer of an electrophotographic light receiving member is constituted by an a-Si material containing from 0.1 to 30 atomic % of carbon as a chemical modifying substance.
Further, Japanese Patent Publication 63(1988)-35026 proposes an electrophotographic photosensitive member comprising, on a conductive substrate, an intermediate layer comprising an a-Si material containing carbon atoms, hydrogen atoms and/or fluorine atoms as the constituent elements (this a-Si material will be hereinafter referred to as "a-SiC:(H,F)") and an a-Si photoconductive layer. This electrophotographic photosensitive member is intended to reduce occurrence of crack or/and removal of the a-Si photoconductive layer without deteriorating the photoconductive characteristics by said intermediate layer comprising an a-SiC:(H,F) material.
However, for the known electrophotographic light receiving members respectively having a photoconductive layer constituted by such a-Si material, although a proper improvement has been made for each of electrical, optical and photoconductive characteristics such as dark resistance, light sensitivity, light responsivity and use-environmental characteristics, as well as aging stability and durability individually, there still exists room for further improvement in view of overall characteristics.
In recent years, high image quality, high speed processing and high durability have been further demanded for electrophotographic apparatus. Particularly, there is an increased demand for further improving electrophotographic light receiving members with respect to electric characteristics and photoconductive characteristics, as well as greatly improve the durability while maintaining high charge retentivity and high sensitivity in any of use-environments.
That is, for instance, in the case of preparing an electrophotographic light receiving member using an a-Si material, if it is intended to provide an improvement for the sensitivity and the dark resistance at the same time, there is often observed a residual voltage on the resultant electrophotographic light receiving member upon use thereof. In addition, when it is used repeatedly for a long period of time, there is a tendency that fatigue due to the repeated use is accumulated to cause a so-called "ghost" phenomenon.
Further, in the case of forming the photoconductive layer using an a-Si material, hydrogen atoms (H), halogen atoms (X) such as fluorine atoms (F) or chlorine atoms (Cl) for improving electric and photoconductive characteristics, boron atoms (B) or phosphorus atoms (P) for control of electric conduction type or other kind of atoms for improving other characteristics are incorporated respectively as the constituent atoms into the photoconductive layer. However, the resulting layer has sometimes become accompanied with defects on the electric or photoconductive characteristics or uniformity of them depending on the way of incorporating such constituent atoms. That is, the photoconductive layer has uneven portions in view of the charge transportation capacity, such uneven portions entail unevenness in the density of an image obtained, which appears particularly remarkably in a half-tone image. In view of this, there is a demand for the film constituting the photoconductive layer to be highly uniform not only in view of the matrix structure but also in view of the electrical and optical properties.
Further, as a result of improvements made recently, for instance, in optical exposure system, developing mechanism and transfer mechanism in electrophotographic apparatus in order to improve the image-forming efficiency of the electrophotographic apparatus, there is a demand for improving the electrophotographic light receiving member to be desirably suited for use in such electrophotographic apparatus. In particular, as a result of the improvement in resolution of an image, their has now been demanded a reduction in so-called "coarseness", i.e., unevenness of the image density in a minute region, and also reduction in so-called "minute blank area", i.e., image defect in the form of a minute black or white dot, in particular, reduction the minute blank area which was used to be substantially not problematic in the past. Further, in the case of forming images continuously, a phenomenon that such minute blank area appears from the initial image may sometimes occur and because of this, there is a demand for reduction in appearance of the minute blank area even after repeated use.
Further, in recent years, in order to reduce the production cost of an electrophotographic light receiving member, there has been made a proposal to form the photoconductive layer of an electrophotographic light receiving member at an increased deposition rate by a film-forming method utilizing a microwave energy, that is a so-called microwave plasma CVD method. However, in this case, there are sometimes found problems that unevenness is caused in the quality of an a-Si film deposited, or fine crack or peeling is caused for the a-Si film due to the stresses in the film, whereby the yield is decreased.